The instant invention relates generally to fuel injection systems, and more particularly to electrically operated diesel unit injectors having a control valve for separately regulating each of the timing and metering of fuel in the fuel injector forming a part of the fuel regulating and distributing system, thereby permitting separate adjustment of both timing and metering of fuel from the various nozzle portions of the injectors in response to engine operating conditions.
Fuel injectors that are driven mechanically from the crankshaft of an internal combustion engine to deliver fuel into the cylinders of an internal combustion engine are well known; see, for example, U.S. Pat. No. 2,997,994, granted Aug. 29, 1961 to Robert F. Falberg. The movement of the crankshaft is translated into a force that periodically depresses the pump plunger via a cam, cam follower, and rocker arm mechanism. Since the rotation of the crankshaft reflects only engine speed, the frequency of the fuel injection operation was not adjustable with respect to other engine operating conditions. To illustrate, at cranking speeds, at heavy loads, and at maximum speeds, the timing and the metering (quantity) function for the fuel injector did not take into account actual engine operating conditions.
In order to enable adjustments to be made in the timing of the fuel injection phase of the cycle of operation, Falberg proposed that a fluid pressure pump introduce fluid into a follower chamber to elevate a plunger and thus alter the position of push rod which operates plunger member of the fuel injector. By selecting the effective area of the plunger, the elevation thereof advances the plunger member relative to the desired point in the cycle of engine operation. The fluid pressure pump is driven by the internal combustion engine, and a lubricating oil pressure pump is frequently utilized as the fluid pressure pump.
U.S. Pat. No. 3,859,973, granted Jan. 14, 1975 to Alexander Dreisin, discloses a hydraulic timing cylinder that is connected to the lubricating oil system for hydraulically retarding, or advancing, fuel injection for the cranking and the running speeds of an internal combustion engine. The hydraulic timing cylinder is positioned between the cam which is secured to the engine crankshaft and the hydraulic plunger. The pressure in the lubrication oil pump is related to the speed of the engine, as shown in FIG. 1.
U.S. Pat. No. 3,951,117, granted Apr. 20, 1976 to Julius Perr, discloses a fuel supply system including hydraulic means for automatically adjusting the timing of fuel injection to optimize engine performance. The embodiment of the system shown in FIGS. 1-4 comprises an injection pump including a body having a charge chamber and a timing chamber formed therein. The charge chamber is connected to receive fuel from a first variable pressure fuel supply and the timing chamber is connected to receive fuel from a second variable pressure fuel supply, while being influenced by pressure modifying devices. The body further includes a passage that leads through a distributor which delivers the fuel sequentially to each injector within a set of injectors.
A timing piston is reciprocally mounted in the body of the injection pump in Perr between the charge and timing chambers, and a plunger is reciprocally mounted in the body for exerting pressure on fuel in the timing chamber. The fuel in the timing chamber forms a hydraulic link between the plunger and the timing piston, and the length of the link may be varied by controlling the quantity of fuel metered into the timing chamber. The quantity of fuel is a function of the pressure of the fuel supplied thereto, the pressure, in turn, being responsive to certain engine operating parameters, such as speed and load. Movement of the plunger in an injection stroke results in movement of the hydraulic link and the timing piston, thereby forcing fuel into the selected combustion chamber. The fuel in the timing chamber is spilled, or vented, at the end of each injection stroke into spill port and spill passage.
All of the above-described fuel injection systems employ hydraulic adjustment means to alter the timing of the injection phase of the cycle of operation of a set of injectors mechanically driven from the crankshaft of an internal combustion engine, and the hydraulic means may be responsive to the speed of the engine and/or the load imposed thereon. While the prior art systems functioned satisfactorily in most instances, several operational deficiencies were noted. For example, the hydraulic adjustment means functioned effectively over a relatively narrow range of speeds, and responded rather slowly to changes in the operating parameters of the engine. Also, problems were encountered in sealing the hydraulic adjustment means, for a rotor-distributor pump was utilized to deliver hydraulic fluid to each of the fuel injectors in the set employed within the fuel injection system. In order to provide a hydraulic adjustment means responsive to both speed and/or the load factor, as suggested in the Perr patent, an intricate, multicomponent assembly is required, thus leading to high production costs, difficulty in installation and maintenance, and reduced reliability in performance.
The commonly assigned U.S. Pat. Nos. to Walter et al 4,235,374 filed Jan. 25, 1979 and to Sisson et al 4,281,792 similarly filed Jan. 25, 1979 discloses a cam driven unit injector having a primary plunger and a secondary plunger spaced therefrom, the space therebetween forming a hydraulic link that is controlled by an electrically operated control valve. The volume below the secondary plunger defines a metering chamber which during certain phases of operation is dumped to a drain line and a supply through a check valve located within the secondary plunger. The volume between the primary and secondary plunger further defines a timing chamber which is similarly dumped to drain through a check valve located within the secondary plunger. The above described injector further includes a nozzle that is hydraulically linked with the metering chamber. Upon pressurization of the fuel within the metering chamber injection begins. Injection is terminated by dumping the fuel in the metering chamber through passages within the secondary plunger. The injector further includes a biasing spring situated within the timing chamber for urging the secondary plunger in a downward position, this action will insure that the secondary piston resides at the bottom of its stroke and is thereby pre-positioned to receive fuel during a subsequent metering portion of its cycle which thereafter urges the secondary plunger upward against the biasing spring to fill the metering chamber with a predetermined quantity or charge of fuel prior to the next injection cycle. While the above patents to Sisson et al solve many of the operational deficiencies noted in the hydraulic systems, the construction of the secondary piston having a plurality of check valves therein is unduly complicated. In addition, utilizing a biasing spring to urge the secondary plunger downward requires greater acceleration force to thereafter cause The commonly assigned patents to Walter et al U.S. Pat. Nos. 4,235,374 filed Jan. 25, 1979 and to Sisson et al 4,281,792 not "The commonly assigned patents to Sisson et al 4,235,374 filed Jan. 25, 1979 and 4,281,792". pressurized fuel within the timing chamber and the metering chamber is dumped directly to the supply, pressure surges are created which can decrease the accuracy of performance of similar injectors that are connected in common to the same supply. Finally, injection termination is slowed since the nozzle will close only after the pressure in the metering chamber has been reduced to a relatively low value.
Thus, with the deficiencies of the known fuel injector systems it is an object of the present injection to employ one electronically operated control valve for each injector utilized within a fuel injection system. The preferred embodiment of the invention uses a two-way control valve. However, other valves such as a three-way control valve may be used. The function of the control valve is to control the timing of the injection phase of operation and also to control the duration of fuel metering into the metering chamber. A further object of the present invention is to provide a unit injector that is characterized as having a rapid nozzle closure. A further object of the pesent invention is to dampen pressure surges that are generated upon dumping the highly pressurized fuel in the metering chamber before these pressure surges reach the supply. A further object of the present invention is to provide a reference of position for the secondary or metering piston that is spaced from the lower extreme of the metering chamber to provide for the more accurate metering of fuel thereto.
According to the specific embodiments of the invention illustrated in the drawings of this application and discussed in detail below, the invention comprises: A cam driven fuel injector having a supply port adapted to be connected to a supply or source of fuel and a drain port. The fuel injector further comprises a body defining a bore; a driven or pumping piston reciprocatively situated with the bore; a metering piston reciprocatively positioned within the bore remote from the pumping piston; a timing chamber defined in the bore between the pumping piston and the metering piston; a metering chamber defined in the bore below the metering piston; a spring situated within a cavity or spring cage remote from the bore; a nozzle, having a needle valve, a nozzle passage surrounding the needle valve and at least one flow orifice; the nozzle extending into the spring cage in biasing engagement with the spring to urge the needle valve to close at least one flow orifice during non-injecting periods; first means for supplying fuel at supply pressure to the timing chamber and to the metering chamber; first dump means for permitting fuel within the timing chamber to be dumped therefrom in correspondence with the motion of the metering piston; first passage means for transmitting fuel from the metering chamber to the nozzle; and second dump means for dumping the fuel within the metering chamber to the supply through the spring cage in correspondence with the motion of the metering piston and for stabilizing the pressure force exerted on the nozzle, during the dumping portion of operation, by the fuel within the spring cage with the pressure force exerted on the nozzle by the fuel within said nozzle passage.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.